PURPOSES : The purpose of this study is to identify the dynamic behavior of a cement concrete paving machine (paver) by measuring its response using accelerometers. This is because the dynamic behavior of pavers affects the quality of data from various applications of IoT sensors, such as laser, ultrasonic, optical sensors and so on. Therefore, it is believed that the understanding of dynamic behaviors can contribute to the effective use of various IoT sensors for the acquisition of real-time quality control data in pavement construction. METHODS : Dynamic signals are obtained using accelerometer sensors to identify the dynamic characteristics of paving machines. The main parameters for acquiring dynamic signals are the status of the machine’s operating or standby conditions, and available locations for attaching various IoT sensors. Time domain data are logged at a particular sampling speed using a low-pass filter, subsequently, they are converted to digital data, which are analyzed on three rectangular axes. In addition frequency analysis is conducted on the measured data for identifying the peak frequencies, via FFT (Fast-Fourier-Transform) using MATLAB. RESULTS : The magnitude of the x-directional vibration is higher than that of any other direction under the paver’s operating or standby condition. However, signals from the smoother beam show that the z-directional vibration is more significant in the operating status. It means that the primary vibration depends on the location. Furthermore, the peak frequencies are quite various depending on the status of a paver and its sensing location. CONCLUSIONS : The magnitude of machine vibration and peak frequencies at each status or location are identified from time- and frequency-domain data. When using IoT sensors for quality control or monitoring pavements in construction, the dynamic characteristics of a paver should be considered to mitigate the interference of signals from the paver body or its elements.

Wireless sensors are more favorable in measuring structural response compared to conventional sensors in terms of them being easier to use with no issues with cables and them being considerably cheaper. Previous tests have been conducted to analyze the performance of MEMS (Micro Electro Mechanical Systems) sensor in sinusoidal excitation tests. This paper analyzes the performance of in-built MEMS sensors in devices by comparing with an ICP sensor as the reference. Earthquake input amplitude excitation in shaking table tests was done. Results show that MEMS sensors are more accurate in measuring higher input amplitude measurements which range from 100gal to 250gal than at lower input amplitudes which range from 10gal to 50gal. This confirms the results obtained in previous sinusoidal tests. It was also seen that natural frequency results have lower error values which range from 0% to 3.92% in comparison to the response spectra results. This also confirms that in-built MEMS sensors in mobile devices are good at estimating natural frequency of structures. In addition, it was also seen that earthquake input amplitudes with more frequency contents (Gyeongju) had considerably higher error values than Pohang excitation tests which has less frequency contents.

Recently, measuring instruments for SHM of structures has been developed. In general, the wireless transmission of sensor signals, compared to its wired counterpart, is preferable due to the absence of triboelectric noise and elimination of the requirement of a cumbersome cable. However, the low-cost wireless MEMS sensor has high noise density and transmits the signal wirelessly, so data transmission delay occurs during measurement. Therefore, the footbridges that was previously measured by a mobile phone in 2014 was remeasured using G-Link-200, iPad and iPhone to compare their performance.

Wireless sensors are more favorable in measuring structural response compared to conventional sensors. This is because they are easier to use with no issues with cables and are considerably cheaper. There are several applications that can be used in recording and analyzing data from MEMS sensor installed on an iPhone. The Vibration App is one of the applications used and there has not been adequate research conducted in analyzing the performance of this App. This paper analyzed the performance of the Vibration App by comparing it with the performance of an ICP sensor. Results show that natural frequency results are more accurate (error less than 5%) in comparison to the amplitude results. This means that built- in MEMS sensor in smartphones are good at estimating natural frequency of structures. In addition, it was seen that the results became more accurate at higher frequencies (5.0Hz and 10.0Hz).

Recently, measuring instruments for SHM of structures had being developed. In general, the wireless transmission of sensor signals, compared to its wired counterpart, is preferable due to its absence of triboelectric noise and elimination of the requirement for cumbersome cable. However, the research on the tall buildings with relatively small vibration levels is insufficient. Therefore, in this paper, we used the wireless MEMS sensor and iPad to compare and analyze the vibration measurements of three tall buildings and two towers.

Recently, measuring instruments for SHM of structures had being developed. In general, the wireless transmission of sensor signals, compared to its wired counterpart, is preferable due to its absence of triboelectric noise and elimination of the requirement for cumbersome cable. Preliminary studies on the continuous vibration measurement of high-rise buildings using MEMS sensors have been carried out. However, the research on the low-rise buildings with relatively small vibration levels is insufficient. Therefore, in this paper, we used the wireless MEMS sensor to compare and analyze the vibration measurements of three low-rise buildings.

With increasing number construction of high-rise building which has about 40 to 60 floors there have been many kinds of problem which related with usage from vibration. To predict response acceleration, it is important to assess correct natural frequency. However, due to the noise of MEMS sensor, it is difficult to measure dynamic characteristic such as natural frequency when measuring ambient vibration using MEMS sensor within cell phone. Therefore, a comparative analysis on vibration measuring applications was performed after measuring ambient vibration of 2 skyscrappers which have height between 133.5~244.3m that are located in Seoul and Observation tower using I-jishin APP with noise reduction function of MEMS sensor in order to verify the effectiveness of low noise type vibration measurement APP.

코골이 및 수면 무호흡증 등의 수면 질환은 정신적, 육체적 피로감을 유발하고 정상적인 활동에 심각한 영향을 미치고 있다. 코골이는 공기가 좁아진 기도를 통과할 때 진동에 의해서 일어나는 호흡잡음이고, 수면 무호흡은 기도 주변의 조직이 이완됨에 따라 기도가 일시적으로 막히게 될 때 일어나는 현상이다. 이러한 문제를 해결하기 위해 수면 중 코골이를 검출하고 이를 경감하려는 많은 시도가 이루어져왔다. 본 연구에서는 수면 중 코골이 신호의 검출에 있어서 오류가 발생되는 원인인 주변 잡음이나 기타 영향을 제거하기 위한 새로운 센싱 시스템과 분석 알고리즘의 개발을 수행하였다. 센싱 시스템은 베개 내부에 내장되는 두 개의 polyvinylidene fluoride (PVDF) 진동 센서를 포함하고 있으며 검출되는 신호를 수집, 저장하는 하드웨어부와 코골이 신호를 판단하는 신호처리부로 이루어졌다. 베개에 내장되는 PVDF 센서 중 제 1센서는 코골이 신호를 검출하고 제 2센서는 코골이 신호 및 주변의 잡음을 검출한다. 본 실험에는 10명의 피험자가 참여하였으며 수면 중 잡음이 발생할 수 있는 다양한 환경 조건 하에서 신호를 검출하여 분석하였다. 그 결과 다양한 잡음환경 하에서 코골이 신호가 코골이가 아닌 잡음에 비해 약 70% 이상의 에너지 값을 가지는 것을 확인하였고 이를 통해 잡음으로부터 코골이 신호를 정확하게 검출하는 것을 확인하였다. 본 연구의 결과는 수면 중 발생하는 코골이의 경감을 위한 베개의 개발과 정량적인 수면상태 평가를 통해 건강한 수면 환경을 제시할 수 있는 숙면 유도 시스템의 개발에도 활용될 것이다.

Early alarm system is to detect slope movement before its collapse for road manager to respond quickly. In this paper, alarm criteria for this system is suggested when vibration and angle sensor are used.

Dynamic characteristics of large civil infrastructures have been monitored for safe operation and efficient maintenance of the structures. To measure vibration data, the conventional system uses cables causing very expensive costs and inconvenience for installation. Therefore, various wireless sensor nodes have been developed to replace the conventional wired system. However, there remain lots of issues to be resolved such as power supply, data loss, data security, etc. In this study, smart distributed sensor node (SDSN) was developed to measure vibration data. The SDSN is basically timely synchronized one-channel data acquisition system. It consists of its local time clock with high accuracy and SD memory card or local data storage. It is designed for temporal measurement, not long-term monitoring, since it can operate several hours using embedded batteries. Laboratoy tests were carried to verify the performance of the developed SDSN compared with conventional wired sensors. Several application examples for large civil infrastructure were also suggested.

본 논문에서는 건축물의 실시간 피드백 진동제어를 위한 기초연구로써, 자체 기술력을 바탕으로 개발된 무선 가속도센서 시스템 및 프로토타입 (Prototype) AMD 시스템을 결합하여 피드백 진동제어 시스템을 구성하고, 모형 건축물을 대상으로 구성된 제어시스템의 기초성능을 평가하고자 하였다. 이를 위하여 본 논문에서는 우선 MEMS 센서 소자 및 블루투스 통신 모듈 기반의 무선 가속도 센서 유닛, 실시간 가속도 응답획득 및 제어법칙에 근거한 제어출력을 구현하도록 구성한 운영프로그램 등을 개발하였다. 또한 AC 서보모터를 이용해 기동되도록 설계한 프로토타입 AMD 및 모터 드라이버 시스템을 구성하였다. 마지막으로 이를 이용해 실시간 피드백 진동제어 시스템을 구성하였고, 2층 모형 건축물을 대상으로 실험실 규모의 진동제어 실험을 수행하여 목적된 구조물의 진동저감 효과를 정량적으로 분석하였다. 실험의 결과, 모형 구조물의 1차 및 2차 공진주파수 그리고 랜덤주파수 등의 실험조건에서 명확한 진동저감의 효과를 확인할 수 있었으며, 종국적으로 본 논문에서 개발한 무선 가속도센서 시스템 및 AMD 시스템이 향후 여타 구조물의 진동제어를 위한 효과적인 수단으로 응용될 수 있는 가능성을 확인하였다.

본 논문에서는 무선 센서 네트워크를 이용한 피드백 진동제어 시스템을 구성하고, 모형 구조물을 대상으로 구성된 시스템의 진동제어효과를 실험적으로 검증하고자 하였다. 이를 위하여 본 논문에서는 블루투스 기반의 무선 I/O 센서 시스템과 스마트 재료를 사용한 전단형 MR 댐퍼를 개발하고, 또한 일정한 크기의 정현파형을 발생시키는 가진기 및 모형 단순보 구조물을 이용하여 피드백 진동제어 시스템의 실험?V을 구성하였다. 진동제어 실험은 가진기를 이용해 보의 1/4 등분점에서 일정하게 가진한 상태에서, 보 중앙점에 수직방향으로 설치된 MR 댐퍼를 이용해 진동을 제어하였으며, 보의 2/4 등분점에서의 가속도 응답을 획득하여 제어효과를 평가하였다. 이때, 제어명령은 보 중앙점에 무선 I/O 센서 노드를 설치하고, 여기서 획득된 가속도 응답이 일정 크기 이상일 경우에 설정된 범위의 전압신호를 MR 댐퍼로 출력하도록 설정하였다. 최종적으로 본 논문에서 구성된 무선 센서 네트워크 기반의 실시간 피드백 진동제어 시스템은 비록 제한적인 명령 체계에서 검증되었지만, 실시간적으로 목적된 제어명령의 발생시킴으로써 구조물의 진동을 효과적으로 감소시키는 것을 확인하였고, 추후 다양한 준능동 제어 알고리즘을 적용한 구조적 응답제어시스템으로의 활용 가능성을 제시하였다.

A quartz crystal analyzer is utilized to monitor the corrosion process of an aluminum surface of a quartz crystal for marine sensor by sea water. A quartz crystal having 2000 a of aluminum layer is installed in a specially designed cell and is in contact with sea water imitated electrolyte solution. While a constant potential is applied to the cell, the resonant frequency and resonant resistance are simultaneously measured using the quartz crystal analyzer. In addition, surface topographs are taken with an atomic force microscope(AFM) and the element analysis of the surface is conducted using an energy dispersive X-ray spectrometer(EDX). The simultaneous measurement of resonant frequency and resonant resistance during the corrosion process explains the change of surface structure caused by the corrosion. The variation of resonant frequency addresses the amount surface metal dissolution. As a conclusion, it is found that a simple measurement using the quartz crystal analyzer can replace the complex monitoring employing large equipments in the investigation of a corrosion process of sensor surface.